# Thread: Focal plane of camera (Lumia 520)

1. Hi,
I am working with Lumia 520 on a camera application. For the project, I will need to calculate the shift in the pixels given the physical shift of the camera. Clearly, I will need to know the dimensions of the focal plane to do so. For finding the focal plane, having the lens to sensor distance and focal length should be enough. From the data given on the website, I found that focal length of the camera is 28mm. Further, it is also given that the focus range is 10cm to infinity.

I am a little confused with this data. The distance between the lens and the sensor will be very small, which will be less than 28mm. This seems a little odd to me, since any object at finite distance should be formed between f and 2f. Perhaps I am missing something important here? Further, if that thing gets cleared, how do I estimate the distance between the lens and the sensor or the lens and the focal plane. I can adjust the manual focus distance, but it is a number between 0 and 1000, which gives me no clue about the physical distance.

2. Hi You could find good explanation here :
http://en.wikipedia.org/wiki/Focal_l...In_photography
http://www.cambridgeincolour.com/tut...era-lenses.htm

You want compute distance only with focus information?

3. Hi yan_,
I have focal length information, information about manual focus, normalized between 0 and 1000 and I know that the least focus distance is 10cm(Data from Nokia website) I wish to calculate the focal plane dimensions using the above information.

Thank you.

4. focal plan dimensions?

5. I'm not sure you can rely on the manual focus being normalized. I'm also not entirely certain that the lens even moves if you reduce from 1000 to 999. You also can't rely on the manual focus having the range 0 - 1000. It currently does for Nokia devices and on the Emulator but e.g. HTC devices report min/max values of 0/22.

As for focal plane dimensions. I believe he wants to calculate the height/width of the rectangle that is currently in focus in the real world. E.g. I focus full format on a book on my desk. Given the focus value returned and knowing the properties of my device's Camera I could then calculate the height and width of the book itself.

6. Hi SB Dev,
The second paragraph in your reply exactly describes what I would need. Can you give me a little lead in this aspect?

7. I basically know what you're trying to do but I have not really worked with this myself so I'm not sure how valuable my information will be. I believe I can help you with at least one part of your original question though. The focal length of digital cameras regularly is given as an equivalent to older 35mm film cameras. That means that if it says 28 mm it's not actually 28 mm focal length but that the focal length of the lens given the size of the image sensor (which is smaller than the 35 mm film) is equivalent to a 28 mm focal length lens used with a 35 mm film.

Basically: as the sensor is smaller the focal length can be smaller as well to achieve an equivalent calculation. I'm not sure if it's clear from my description what I mean?

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